Conventionally, a dual-clutch device is known, in which two clutches capable of connecting and disconnecting a power transmission from a driving source, such as an engine, by means of a pressure of a hydraulic oil are provided therein and also a driving power transmission path from the driving source to a transmission is switched between transmission lines, each of which is formed via one of the clutches.
Engaging and disengaging of each of the clutches of such a dual-clutch device are controlled by adjusting an amount or pressure of the hydraulic oil to be supplied to each of the clutches.
Although being different from the clutches configured to perform connecting and disconnecting of a driving power from the driving source as described above, another technique on a clutch controlled by a hydraulic oil is known, in which clutches, which are configured to switch combinations of gears in a transmission gear mechanism to be used to transmit a power, are filled with a hydraulic oil in such a manner that a pressure in a clutch when downshifting is performed becomes a standby pressure (e.g., see Patent Document 1).